As reserves of easily accessible oil become more scarce there has been an increasing trend to look towards other sources of hydrocarbons in order to meet current needs for fuels and other petrochemical products. It has been known to utilise GTL technology in order to convert natural gas into heavier hydrocarbons. Natural gas is currently readily available in a number of locations that are easily accessible and, as a result, it represents a promising starting point for hydrocarbon conversion.
Dry natural gas, after extraction of liquid petroleum gas (LPG) and optionally ethane, can be transported either by pipeline or as liquid natural gas (LNG) or may be readily converted at the location of gas production to heavier liquid hydrocarbons via the GTL process. The GTL process is based on Fischer-Tropsch synthesis. The resulting GTL products include a wide variety of hydrocarbons that can be transported more easily than LNG.
There are significant new GTL projects—particularly in the Arabian Gulf region—that are currently coming on stream and will be expected to produce in excess of 200,000 barrels/day of GTL products by the end of 2020.
GTL products typically have a paraffinic nature which provides these products with special characteristics. They are virtually free of sulphur and aromatics and have a high cetane number making them particularly desirable as fuels. The typical output from a GTL process may include condensate, light paraffins, naphtha, middle distillates and base oils. The middle distillate products typically include paraffinic kerosene and diesel. For fuel products of GTL conversion there is a need to blend with conventional crude or condensate derived products in view of the required properties for end use, such low density as the density of GTL fuels is generally low. In 2009 the first synthetic paraffinic kerosene was approved for use in the aviation industry and comprised a blend of conventional aviation jet fuel with 50% GTL derived kerosene. In October of 2009 Qatar Airways jointly with Shell and Rolls-Royce flew the first flight from London's Gatwick Airport to Doha in Qatar fuelled entirely by a GTL fuel blend.
There is a need for producing high levels of GTL middle distillate products that can be used as a basis for fuel blends and for other paraffinic hydrocarbon based products. There exists an ongoing need for improved GTL processes in general. In addition, there is a need for increased utilisation of condensate obtained as a by product of natural gas extraction within the existing GTL processes or as a by product of other natural gas processes such as LNG production.
US-2005/0252830-A1 describes processes for introducing condensate recovered from a natural gas extraction process into the liquid fraction of a product derived from a high temperature Fischer-Tropsch reactor and subsequently processing in a hydrotreater. The process described in US-2005/0252830-A1 is intended to occur after GTL processing of a natural gas feedstock has occurred, and as a result, requires additional levels of fractionation prior to initiation of the described process. Practical application of the described process is limited as it requires additional levels of equipment to be introduced to a conventional GTL process.
EP-1853682-A describes a catalytic conversion of a combined stream of condensate and paraffins obtained from a Fischer-Tropsch reaction in order to prepare a lubricating base oil. EP-1853682-A does not describe processes for the preparation of middle distillate products and is concerned primarily with production of heavier hydrocarbons for lubricating base oil purposes.
It is an object of the invention to provide an improved process for GTL preparation of middle distillate products that includes utilisation of condensate produced as a by-product of natural gas extraction.
It is a further object of the invention to provide improved GTL performance particularly with regards to the conversion of heavy paraffinic hydrocarbons into shorter chains via the process of cracking.